1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member widely used for copying machines, printers, engraving systems, and the like apparatuses. The present invention relates also to an electrophotographic apparatus and a process cartridge employing the above electrophotographic photosensitive member.
2. Related Background Art
Conventionally, an electrophotographic photosensitive member directly undergoes electric or mechanical action in the processes of electric charging such as corona charging and roller charging, image development, image transfer, cleaning, and so forth, and is required to have durability against the above action.
Specifically, the electrophotographic photosensitive member should be resistant to abrasion and scratching by friction on the surface, and to electrical deterioration. In particular, in a charging system like a roller charging system utilizing electric discharge, the photosensitive member should be durable against high energy arc discharge.
Further, there are some problems of the toner attaching to the surface of the photosensitive member caused by the repeated development with the toner and the repeated cleaning of the photosensitive member. To cope with the problems, the surface of the photosensitive member is required to have improved cleanability.
To satisfy the above requirements for the photosensitive member surface, a surface protection layer mainly composed of a resin is provided. For example, Japanese Patent Application Laid-Open No. 57-30843 discloses a protection layer in which a particulate metal oxide is added as electroconductive particles to control the resistance.
Besides the protection layer itself, incorporation of an additive into the charge-transporting layer is studied to improve the properties of the photosensitive member surface. For example, the following silicone resins having a low surface energy are reported as the additive:
silicone oil (Japanese Patent Application Laid-Open No. 61-132954), PA1 polydimethylsiloxane, PA1 powdery silicone resin (Japanese Patent Application Laid-Open No. 4-324454), PA1 crosslinked silicone resin, PA1 poly(carbonate-silicone) block copolymer, PA1 silicone-modified polyurethane, and PA1 silicone-modified polyester. PA1 powdery polytetrafluoroethylene, and PA1 powdery fluorocarbons.
The typical polymer of a low surface energy includes fluoropolymers. The fluoropolymers below are useful as the additive for the photosensitive layer:
However, a surface protection layer containing a metal oxide or the like, which has a higher hardness, tends to have a higher surface energy to result in lower cleanability and other shortcomings. A silicone type resin, which is advantageous as the additive in lowering the surface energy, is less compatible with other polymers, and as a result, when the silicone resin is incorporated into the photosensitive member, such resin tends to agglomerate to cause light scattering, or tends to bleed out and deposit to the surface to render unstable the properties of the photosensitive member, disadvantageously. A fluoropolymer typified by polytetrafluoroethylene (PTFE) has a low surface energy, but is insoluble in solvents and less dispersible, producing a less smooth surface of the photosensitive member. Further, the fluoropolymer has a low refractive index, causing generally light scattering and deterioration of the latent image thereby.
High polymers like polycarbonate, polyacrylate esters, polyesters, and polytetrafluoroethylene are generally less resistant to arc discharge, and readily deteriorate by fission of the polymer main chain by electric discharge.